What’s up with the 90 day limit?

(CNN) – People who have been fully vaccinated can now be quarantined if exposed to COVID-19, according to new guidelines from the Centers for Disease Control and Prevention. But the agency acknowledges there are many researchers who do not know how the vaccines affect the transmission.

The new quarantine exemption applies to those who:

• Had both doses of the vaccine.
• Had the last dose between two weeks and three months ago.
• Does not show symptoms of coronavirus infection.

“It is important to note that CDC does not indicate that a person who has been vaccinated will not be able to distribute COVID-19 within the first 90 days after being fully vaccinated. vaccines do not expire after 90 days, “said a CDC spokesman. Kristen Nordlund told CNN. “The three months are in line with what the CDC is currently recommending for people with a natural infection, and we will continue to evaluate this period as we learn more about the duration of protection against the vaccines.”

She added: ‘There is currently limited information on how many COVID-19 vaccines can reduce transmission or how long the protection period lasts. However, we know that quarantine can be very disruptive for the individual as well as society. The benefits of avoiding unnecessary quarantine, specifically for those who have been fully vaccinated, probably outweigh the unknown risks of transmission from a vaccinated person. ”

The quarantine exemption does not mean that people who have been fully vaccinated can stop wearing a mask, keep their distance from others and follow other CDC guidance. They are also not exempt from test requirements when returning from abroad.

Can people without symptoms, fully vaccinated, transmit the virus?

Although the guidelines imply that people who have been vaccinated are less likely to transmit the virus, the CDC makes it clear that vaccination trials have largely focused on the prevention of symptomatic cases of Covid-19. This does not mean that humans can not catch the virus and spread it asymptomatically, but it is significantly more difficult to measure, experts say.

Measuring the transmission of Covid-19 directly is difficult, so researchers are using proxies to estimate how likely someone is to transmit the virus.

One possible proxy is viral load – how much virus people circulate in their bodies. Research has shown that people with lower viral loads are less likely to transmit the virus.

A recent study in Israel found that people who were infected 12 to 28 days after their first dose of Pfizer vaccine were four times lower than when they were infected in the first twelve days. Although the study has not yet been reviewed by a peer and does not contain the data after the second dose, Megan Ranney, associate professor of emergency medicine at Brown University, is considered ‘very exciting’.

“This indicates that you are less likely to pass it on to others after the first few weeks, even before you are completely immunized,” she said.

Another study on the AstraZeneca vaccine also suggested that it may affect transmission, but this was done using a different measure. The researchers collected nasal swabs from the trial participants in the UK each week and found that the rate of positive tests after two doses of vaccination dropped by half.

None of these studies directly measured the transmission – for example, by locating contact from study volunteers to see if they became infected. But it gives a positive sign of what experts have been suspecting for some time, based on experiences with vaccines for other diseases.

“It assumes, I think, that the vaccines also interrupt the asymptomatic transmission.”

“I think it’s probably true,” he said, adding, “I do not know that all the i’s are dotted and that the intersections have been crossed.”

More studies testing people who are regularly vaccinated for Covid-19 will give doctors a better understanding of how vaccines affect transmissibility, and for how long, Ranney said.

This is partly why the recommendation only applies for up to three months, because the CDC and vaccine manufacturers do not have much more information than people have vaccinated. “Vaccinations will definitely last longer than three months,” Hotez said.